The death certificate that Brody is typing for the first victim states that her death occurred at 11:50PM, but the sun was obviously shining when she entered the water. Also, the time of discovery of the body is stated as 10:20PM, but it is obviously the next morning when her body is discovered (Brody had just gotten out of bed when he received the phone call at home).
When Quint hooks something "big" with the rod on the Orca, and we cut to a close-up of him, the line is heard running from the reel, but on the right-hand side of the screen you can see the line hanging loosely in the eyes of the rod.
As the shark passes the Orca and Chief Brody fires his gun at it, the second gun shot can be seen hitting the water before the gun fires it. It happens immediately following the cut after the first gunshot.
When Hooper is examining Chrissie Watkin's corpse, he attributes the attacking squalus (shark) as Longimanus or Isurus Glaucus. Carcharhinis Longimanus is the pelagic White Tip Shark, and wouldn't come close to shore. Its bite would never be mistaken for a great white's. Isurus Glaucus is a Short Fin Mako, and is only found in the Pacific Ocean, not the Atlantic, as the Isurus Oxyrinchus would be.
As Brody argues with Mayor Vaughan about keeping the beaches closed over the Fourth of July, he states that five people were chewed up in the surf (in New Jersey) in five days, in 1916. In fact, it took place over a twelve-day period, and three of the victims were attacked in a tidal creek.
After Chrissy Watkins' remains were pulled out of the cabinet in that little pan, Hooper went on to record his findings of the remains. There is no way all of the remains he described into his tape recorder would fit into that little, shallow pan.
Sheriff Brody learns from his deputy that the boy scouts are doing their "Mile Swim" in the bay for their merit badge. While the Boy Scouts of America do offer a "Mile Swim" patch for those scouts able to swim, non-stop for that distance, there is no merit badge that requires swimming a mile. (An Eagle Scout like Steven Spielberg should have known that.)
When Hooper first meets Quint, Quint asks him to tie a sheep shank. Hooper ties a knot and tosses it to him. However, the knot Hooper ties is actually a trumpet knot, not a sheep shank. They both serve the same purpose (shortening a length or rope) but they are tied differently and have a slight difference in appearance.
In Quint's Indianapolis story, he says the ship was on its way back from delivering the atomic bomb, from the island of Tinian to Leyte. In fact, the Indianapolis, after having delivered a part of the bomb at Tinian, returned to Guam, where it lay over for two days before departing for its next mission to Leyte - an entirely separate mission. Further, Quint states that they didn't see the first shark for half an hour. This is incorrect from statements of survivors, and especially considering the fact that the Indianapolis was hit by torpedoes at 12:02 a.m., July 30, 1945. Even at dawn, the men suffered photophobia from the sun reflecting off the oil which covered them and the water. Further, there was no shark attacks on day one after the sinking. Also, the statement by Quint that no distress signal was sent is wrong, since the Indianpolis, on a new mission after having successfully delivered its cargo to Tinian and returned to Guam, was no longer under radio silence and did indeed send a distress signal. These three errors are commonly misstated, as the urban legend became that the Indianapolis was sunk upon its return from delivering the bomb.
When Hooper is gutting the Tiger shark, the order of things he pulls out does not match the order that, when they land at Brody's feet, as Hooper throws them towards him, and some things just appear at Brody's feet.
When the Shark first approaches Hooper in the cage, the above water shot shows the barrels being towed through the water at great speed. However, underwater the shark passes Hooper at less than half the speed of the barrels, and the shark has no (barrel) lines attached.
When Chief Brody and Hooper tie the ropes to the stern cleats, Quint shoots a harpoon under the shark's mouth. When Hooper is in the shark cage, look at the shark's mouth when it passes by. There is no harpoon there.
When Jaws attacks Hooper's cage, there is live footage of a real Great White with a rope hanging from its mouth. This shark's mouth is clearly much smaller than Jaws' mouth when it attacks the boat moments later.
Hooper wears glasses (old fashioned rimless) throughout the film, but the temples (the part that goes from the glasses themselves to the ears) change from time to time, even within the same scene. Sometimes they are connected to the glass part of the frame at the top, and sometimes in the middle.
As the camera is zooming in on Quint as he gives his speech at the town meeting, there are two women, one wearing blue and the other black, seated next to each other. When it cuts to the shot of people in the room listening to Quint, the woman in blue is still there, but the one in black has disappeared.
During the town meeting, the shot before Quint scrapes his fingers over a chalk drawing of a man-eating shark on the blackboard shows the back of the meeting room, including the blackboard. There is no drawing, and Quint is not in the shot, even though both are there a split second later.
When Chrissy's body is found on the shore, it has been severely damaged by the shark attack, but is still mostly intact. When Hooper does his autopsy, there are far less bodily remains than were found on the beach.
Before Alex Kintner is attacked, Sean Brody is shown sitting on the beach singing. After Alex is attacked and people are running out of the water, Sean can be seen standing on the beach, and in one shot, Chief Brody can be seen grabbing him. But a couple of seconds later, Sean is shown sitting on the beach in the same spot he was before, as if he had not moved.
When the two old fishermen are fishing for the shark from the pier, the shark takes the bait and you can see the chain getting pulled into the sea. In the next shot you can still hear the chain being pulled into the sea but if you look on the pier, you can't see any chain being dragged in and the wooden post that the chain is secured to changes into a different position.
On the Fourth of July, Sean (the youngest Brody kid) is wearing a white t-shirt with orange around the collar, and green shorts. But after Michael goes into shock and Sean is seen crying, he's suddenly wearing darker shorts and a plain white shirt with no orange. Later at the hospital, he has his orange and white shirt and green shorts on again.
When Hooper and Quint are comparing their scars, Hooper shows him a large scar on his left forearm. Later on (climbing down a ladder), when the boat engine has died and Hooper has his sleeves pulled up, the scar is gone.
When the two little kids who pull the fake shark fin around, finally surface, they find themselves surrounded by the Coast Guard's boats and rifles: the kid on the left then takes his mask off and removes his headgear (a diver's cap). But, just a second or two later, when he's being hoisted into one of the surrounding boats, the cap is back on his head, in its original position.
When Brody boards the ferry and tells them to take him out to the Boy Scouts in the water, Larry Vaughn also boards the ferry. Although the ferry driver has not been given new instructions, he takes them all over to the other side to the ferry terminal, ignoring Brody's initial request.
When Hooper is in the shark cage he removes the cork from his spear that holds poison, then when the shark hits the cage he loses his spear and as it floats through the water the cork reappears, then the next time you see the spear hit the ocean floor the cork is gone again.
In the scene where the two fisherman are trying to catch the shark with the holiday roast on the pier, it is very dark outside yet when it cuts to Brody (the scenes go back and forth proving that it takes place in the same evening), it is still very light outside.
When Quint is hauling in the rope from the first barrel and the shark appears suddenly, he jerks back in surprise and still has the rope in one hand only. The next shot shows the rope flying out of both hands, which are cut by the force.
During Quint's speech at the town meeting during which he offers to kill the shark, there is an obvious shift after he warns them they could be on Wellfare. When the camera cuts back to him as he begins, "I don't want no volunteers," his hair and sideburns are longer, his shirt collar is disheveled, the audio has a slight echo, the chalkboard has moved about a foot to the right and its drawing has slightly changed, the room behind him is completely different; the furniture and papers posted on the wall are different, and Quint's own shadow and the shadow of a citizen on the left wall are different, indicating that the lighting has shifted. This last line was clearly shot at a different time and edited back in.
Brody, Hooper, and Quint get soaked when the shark is pulling the boat backwards, but in the next shot, with Quint still wielding the machete above his head (after having cut the ropes), they appear dry. When the shot returns to a close-up of the three men, they're wet again.
When the three men are in the cabin of the Orca at night, Quint is leaning forward against the table and is drinking something. In the next shot, as Chief Brody feels the cut on his forehead, Quint is turned towards the side leaning on the back of his seat, but in the next shot of Quint, he is leaning forward again in the same position as the first shot.
When Hooper visits Brody's home, he brings two bottles of wine. Brody pours himself a large measure, and then gives his wife and Hooper some. If you look at the bottle, firstly it seems rather full for the amount he's just poured, and secondly the level changes from shot to shot. Sometimes it's above the label, sometimes below.
Just before the Kintner boy is attacked, when Chief Brody is sitting on the beach watching the water, he speaks with the old man called Harry. In the close-up shot of Harry the chin strap of his rubber cap hangs down loose at his chest, but in the side shots the chin strap is tucked up at his ear.
When the shark eats the guy in the red boat in the pond, Brody grabs a red blanket and goes for a brown blanket after exclaiming, "He's in shock," in reference to his son's close encounter with the shark. In the next shot, his wife is laying down blue and brown blankets over Michael.
Brody asks Hooper to help with the group of men crowding into a small boat. Hooper says that the officer wants him to tell them that they're overcrowding the boat. They show the men climbing in and there's a guy in a blue jacket climbing down the ladder into the boat. He waves his arm and says, "What do you care?" They then show Hooper asking if they know a good restaurant or hotel on the island. When they show the men again, uttering the line "Yeah, walk straight ahead," the man in the blue jacket is on the deck again and is again descending the ladder.
When Michael and his two friends are sitting in their boat, in the pond, in the first close-up they sit on the white wrinkled up sail, but in the next wide-shot two of them sit on the spread out blue tarp.
When the pump is given to Brody, Quint says, "Pump it out, Chief," and then Quint, with his long blue sleeves, thrusts his machete into the side of the boat. However, in the close-up Quint's arm has no sleeve whatsoever, as the machete meets the wood.
When there is a false alarm in the water, a lady screams when she sees the fin. Behind her there are a girl and a boy on a blow-up raft. In the next shot a man is seen in a similar position, and behind him, there is now an extra girl on the raft.
Chief Brody pulls his son out of the water, who is in shock after a close encounter with the shark. His pants get very wet as he splashes through the shallow water and we see a bunch of wet spots. Cut to Brody laying the boy onto the sand, and the wet spots are in a completely different arrangement. Areas that were wet a second before are now dry and vice versa.
When Chief Brody is in the hardware store getting supplies to make "Beach Closed" signs, there are two buildings across the street (visible through the shop window), painted dark gray/blue, with large windows trimmed in white. When the chief exits the building and stands on the curb right out front loading the supplies into the deputy's car, the building across the street is a large brick building with small windows.
When Hooper, Brody and Quint are preparing the cage for Hooper's confrontation with the shark, overhead shots show that the deck of the boat is dry. But scenes before and after show a few inches of water in the boat, a result of the shark battering in the Orca's side.
When Hooper and Brody are tying off the ropes on the back of the boat and Brody traps Hooper and pulls him free, the rope breaks when it snaps back. Yet in the next shot it's still tied around the boat.
When the mouth of the tiger shark is first opened on the dock there is blood on the mouth and in the back of its throat. After it has been hung up and when one of the boaters puts his head in its mouth, there is no blood.
The sun's position over the water, and subsequently the lighting, often changes from shot to shot - very noticeably when the kid surfaces with his fake shark fin, and in several scenes aboard the Orca.
In one of the first scenes scene when Quint stands at the bow of the boat to shoot the shark with a harpoon, he takes aim at eye level with the camera behind him. But when the camera cuts in front of him he is shooting from hip level
When the engine of the Orca is blown, you see Hooper jumping into over a foot of water, and the entire engine compartment is flooded. In the next shot, you see Quint reaching for, and using a fire extinguisher to put out the fire in a dry engine compartment.
When Brody is doing the chum line for the second time you see that his cigarette has been lit for some time, yet when he has just seen Jaws for the first time and tells Quint, "... you're gonna need a bigger boat..." he is clearly smoking a freshly lit, full length cigarette.
When Crissy's remains are found on the beach. The initial shot of the remains show crabs crawling on them, and then another crab is dropped on the remains from above, right before Sheriff Brody approaches.
When Quint notices his rod starting to click, the rim of the reel has a shiny metallic coloration that reflects the sky, but when he is hooking it up to his vest a few seconds later, the reel has a dull gray metallic coloration which doesn't reflect a thing.
When Quint shoots the second barrel onto the shark you can clearly see three barrels remaining on board. Just over a minute later when they are chasing the shark and Quint yells "run him down Hooper" it looks from the shot onscreen which is from about 40-50 metres away, that there are now four barrels on board.
When Quint yells "untie this, he'll pull out the transom" a shot from inside the boat shows the next barrel (which has been shot onto the shark) move from the front of the boat and you can see that there is just one barrel remaining. But a few seconds later when the shark begins pulling the boat backwards, there are now two barrels remaining.
While Brody is sitting on the beach watching the lady in the water, several items next to him on the left of screen, and the bottom of a blowup raft which can be seen under the door of the changeroom behind him, disappear between shots, while a blue esky suddenly appears next to Brody.
When the engine of the Orca explodes and the shark swims away, Brody is shown standing on the bridge, then when the camera pans down to Hooper standing below him on the stern, the iron ladder, used to climb on and off the bridge, has disappeared. When Quint comes out and hands Brody and Hooper a life jacket, the ladder has returned.
At the Hospital, when Ellen leaves with Sean, Brody looks over and sees Larry standing at the reception. In the next shot when Brody approaches Larry, a black ashtray, which was not there in the previous shot, has appeared on the counter.
During the town hall scene, Mr. Polk (next to Larry) is leaning forward against the bench, as are most of the other selectmen. However in one shot from behind the selectmen, he is leaning so far back that he cannot even be seen, but in the next shot, still on the men, he is back leaning forward.
When Brody, Hooper and Quint encounter the shark for the first time, the direction which the shark approaches from is inaccurate. When Brody and Quint walk out on deck, they along with Hooper look towards the port side, like the shark is approaching from that direction. In the next shot from behind Brody and Quint, the shark is approaching from the starboard side, then the three men are all looking towards port side again, before the shark swims past the stern coming from starboard side again.
When Brody asks the ferry driver to take him over to the kids out swimming, the word "Amity" appears in big dark letters on the front of the ferry above the water. When it gets to the other side, the ferry is facing the same way, but the word "Amity" no longer appears at the front. This must be a different ferry to the one seen originally.
Just before Quint shoots the first barrel into the shark, Hooper has the camera
around his neck. He hurries around the starboard side of the boat and a
second later goes into the cabin without the camera around his neck.
When the shark first shows up on the boat we see Hooper and Brody go to the front of the boat and they are both wearing sneakers. But when we see Brody going out to the edge of the barrels he's wearing boots.
When Chief Brody throws the air tank into the sharks mouth, he throws it in bottom first meaning the valve part is sticking out of the sharks mouth. Later, when the shark is charging him and Chief Brody is shooting at the tank, it's reversed and now the bottom of the tank is sticking out of the sharks mouth.
When the shark starts to pull the Orca backwards, a towline is clearly visible running from the stern of the Orca (to the tow/camera vessel), in spite of the attempted use of the rope lines from the yellow floats to cover it.
When the two barrels pop up out of the water, there is a cut to Brody and Hooper then a cut back to the barrels with the orca in the background. In this shot, Quint is on the bridge while Brody and Hooper are at the stern, but if you look closely you can also see a crewman moving around inside the cabin.
On the TV/video version of Chrissie's death scene, a fine wire can be seen connected to the buoy as she is being shaken about by the shark. This was probably used to stop it drifting out of shot. The wire has been removed on the DVD version.
When we get the first underwater shot of Hooper in the cage there are air bubbles floating to the surface in the top right of the screen. One could assume they are from the safety divers below the cage.
When Brody, Quint and Hooper are watching the shark coming towards them after seeing it for the first time, following the cut to Hooper on the bridge, for a brief moment, shadows of the cameraman and crew members can be seen on the shark as it approaches the stern of the boat.
Like Quint said, "Black eyes. Like a doll's eyes. When he comes at ya, he doesn't even seem to be livin'... 'til he bites ya, and those black eyes roll over white and then..." So for all those scenes where we see Jaws attack someone, like Quint or the guy in the pond, his eyes should have rolled back as a way to protect them.
When Brody is left on the boat by himself the 3000 psi scuba tank floats beside him. A full scuba tank would sink. Only an empty tank would float because it does not include the weight of the compressed air inside. For the tank to explode however, it would have to be full and pressurized.
When Hooper finds the shark tooth in the hull of Ben Gardner's boat, the point is sticking up, with the root end of the tooth embedded in the wood. If the shark had lost the tooth while biting into the hull, Hooper should have found the point stuck in the wood, with the root end exposed.
When Brody and Hooper are out on Hooper's "High Tech" boat, there is a radar antenna rotating on the bow of the boat. A radar antenna should be at the highest point possible on a boat. In the position shown on Hooper's boat, there would be no radar coverage behind the boat as it would be blocked by the cabin and bridge of the boat.
Some think that when Quint first encounters the shark, he incorrectly refers to the Great White shark as an orca, saying that he's "gotta get a good shot at that orca's head". In fact, as he referred to the great white when first approached by Hooper and Brody inside his boathouse, he is calling it a "porker" - slang term for "big & white" - but with his accent it sounds similar to "orca".
Real great white sharks do not behave in the manner depicted in this
film. In fact, unprovoked shark attacks are very rare, with only a handful of them being fatal and two out of three people survive a great white shark attack. However, this is a thriller/horror movie and many things are intentionally exaggerated to fit the genre.
When Hooper is examining Chrissie's body he attributes it to an attacking squalus. Squalus is genus of dog sharks. He should know this, being a shark expert. However, at this point, Hooper does not know what kind of shark attacked her and so he is listing all of the species it could be. (He also indicates Longimanus and Isurus glaucus, which are whitetip and mako sharks, respectively.) More than that, though, "squalus" is the Latin word for "shark" and is often used by marine biologists as a generic name for sharks.
MythBusters discovered that the shark was incapable of pulling the boat backwards by the cleats. To do so the shark would have had to pull twice its own body weight. However, this is a thriller/horror movie, and shark's strength is intentionally exaggerated to make it appear invincible.
When Quint stabs the machete into the Orca's gunwale, the wood has already been marked up with gashes from the machete, probably from previous takes. However, it is conceivable that this was not the first time Quint has done this, and the marks in the wood were not a mistake.
During the barrel scene, the shark pulls three barrels underwater. MythBusters discovered that the shark would have had to exert 1200 pounds of pressure, which it would be incapable of doing. However, this is a thriller/horror movie, and shark's strength is intentionally exaggerated to make it appear invincible.
When Mike shows up at the beach Martin asks him to go to the pond instead with the boat and friends. Then when the kids pull the fake shark stunt and everyone is running out of the water we see Ellen calling for Mike. But when she goes up to Martin she tells him that he's in the pond. How did she know that?
The corners of Jaws' mouth change throughout the movie, whether we are seeing a footage shark or the mechanical one. When we see a real one, the lines of its mouth are parallel. But when we see the fake one, the top corners of its jaws are overlapping the bottom ones.
Later in the movie the shark is chasing the fishing vessel Orca after the intrepid crew has harpooned it and put "three barrels" on him, which are clearly seen following them in the background of the shot. What is also clearly seen in this shot is the wake from the towline that attaches the barrels to the fishing vessel itself.
When the shark jumps onto the boat, you will notice daylight shining through his gills. The sharks used for filming included a right and left design. Which meant one side had skin and the other side didn't. This design allowed the daylight to shine through to the other end and through the gills.
After Quint chops the rope to stop the boat from being pulled by the shark, a calm moment follows during which the men are just catching their breath. After a few seconds, three barrels suddenly appear, but during that time, you can see the barrels in the foreground just under the water, waiting to be released and pop to the surface.
The shots from under the water of Chrissie swimming show a brilliant light above her, but the sun is on the horizon and a first quarter Moon wouldn't be that bright. It can't be from a full Moon either as that would be opposite the Sun in the sky, and so it could not be overhead whilst the Sun is on the horizon.
As the camera begins to zoom in on Quint after he scratches the blackboard at the town meeting, Brody can be seen kneeling down to stay out of shot on the lower right of screen. Then ten seconds later his shadow is seen on the blackboard as he stands up.
During the scene at the hospital after the shark attack in the pond, as Michael and his bed are being wheeled out of the room and down the hall by a female nurse and a male doctor the actor playing the male doctor looks directly into the camera.
When the shark attacks a character, his severed leg floats to the bottom of the water. When the leg hits the bottom, it doesn't behave like a leg with a real knee joint. The knee joint doesn't bend at all on impact with the bottom, for instance.
One of the first scenes in which the shark engages the boat- Orca , you see Brody, Quint and Hooper fall to one side as the boat tips to the side. If you watch closely, it appears that the actors appear to fall over, prior to the boat actually tipping over ,as if they are anticipating the effect.
When the shark swims out from under the Orca after nearly tipping it, the "sea sled" apparatus is visible under the mechanical shark, including the tow cable which is very visible pulling the shark from ahead of it and to its left.
The goof items below may give away important plot points.
The first victim in the film is the female student named Chrissy. We see some of her remains being discovered being eaten by crabs and this occurs in daylight. According to the Police report Chief Brody prepares at the typewriter the time of her death is 7-1-74 (Monday 1 July 1974) at 11.50pm. The time the deceased was discovered is listed as the next day, 7-2-74 at 10.20pm (not am - first error). The second victim in the film is the Alex Kintner boy. According to the reward notice posted by the boy's mother, he was killed on Sunday June 29th (no year given - but surely must be same year as the first victim). Therefore, the second victim in the film was killed before the first victim, going by the dates given (second error). Finally, when one checks the calendar 29 June 1974 was in fact a Saturday, not a Sunday (third error).
When Hooper climbs into the cage he is not wearing fins, yet when he is lowered in the cage, in the very first shot underwater, he is wearing fins. In the following shots he is not wearing fins, but after the shark destroys the cage and he swims to the bottom of the ocean, he is wearing fins once again.
In the close up scene where Hooper is in the shark cage, Jaws attacks and bends the bars on the cage out of shape. After Hooper exits the cage and swims to the bottom of the ocean, the shark is shown attacking an empty cage with all the bars perfectly in line.
When Quint and co. are tracking the shark, they use harpoons tied to barrels to tire the shark. When the shark is approaching Brody, who sits on the foremast waiting to shoot it, the surface of the water is visible behind it and the barrels are gone in two shots. The barrels are also gone when the shark blows up.
Quint removes a cap from one of his teeth when they're swapping stories about injuries below deck. The cap is out for the rest of the movie until he's being eaten by the shark, when the cap is back in place.
When Hooper causes Ben Gardner's head to drop into the hole in the boat, it falls halfway out of the hole. After a quick cut away to Hooper's reaction, the head next appears further back inside the boat.
Alex Kintner was killed sometime on Sunday, June 29th (according to the notice on the board at the town meeting). On the evening of the next day (Monday) Ellen Brody says that her son probably wouldn't go in the water again "after what happened yesterday." The next day (Tuesday) Hooper arrives and the tiger shark is caught. Hooper proposes to cut it open to see if it is responsible for the deaths. He specifically states, "The digestive system of this animal is very, very slow. Let's cut it open. Whatever it's eaten in the last twenty-four hours is bound to still be in there and then we'll know." However, more than twenty-four hours have elapsed since the last known victim, Alex Kintner, was killed.
When Brody blows up the shark, off in the background there is land in some shots and then no land in others. At one point, there is land about half way across the horizon, then there is land across the whole horizon, and then no land, it varies shot to shot.
There are five barrels on the Orca and four get shot into the shark, but the first is later removed. This occurs just before Quint destroys the radio. The barrel is no longer attached to the shark and just as Quint says to Brody "where are you going", Hooper is shown on the right of screen holding the barrel. When we next see Hooper he is putting the barrel back with the others just as he sees Quint through the window destroying the radio. This means all five barrels should be on the orca at this moment but when we next see the barrels there are only four when there should be five.
When the Chief and Hooper are trying to convince the Mayor to shut down the beaches, Chief Brody says there have already been two deaths. But, in fact, as of that time in the movie, the girl on the beach, the Kintner boy and Ben the fisherman are all dead. (However, this continuity mistake is somewhat understandable since the scene with Ben's head rolling into view of his destroyed boat was actually filmed after the movie wrapped - having been filmed in the film editor's swimming pool. So, when Chief Brody made that statement to the Mayor, there may have actually been no real proof of the death of Ben since it was actually filmed much later.)
The sign at the town meeting states Alex Kintner was killed on a Sunday (June 29). At the end when Brody and Hooper are paddling back to shore, Hooper tells Brody it is Tuesday. Six days have passed since Alex was killed, which would mean the present day is a Saturday, not Tuesday.
When Hooper is searching Ben Gardner's boat, when he sees the head, he drops the torch, knife and shark tooth. In the shot from underneath, only the torch and knife are seen sinking to the bottom, the tooth is nowhere to be seen.
Towards the end of the film, there is a medium shot of the rear of the boat when Jaws comes right out of the water. If you look carefully under the shark model as it leaves the water, you can see the mechanical wheel they used to maneuver the model.
While hitting a shark in the nose MAY drive the shark away if it's attacking you, once a shark has you in its jaws, especially a large shark of more than six or seven feet (as in the case of Jaws), hitting it in the nose is not a guarantee that the shark will leave you alone and may in fact just anger it and make it more aggressive. So Quint hitting the shark in the nose would not necessarily drive it away.
When Quint is in the shark's mouth, you can see a soft white mat, under Quint, to protect him, and to make sure he is comfortable. This same white mat can also be seen under his shirt, acting as his "skin" as he's bitten.